1. Field of the Invention
The present invention relates to a silver halide photosensitive material. More specifically, the present invention relates to a silver halide photosensitive material having a high speed and an excellent storability.
2. Description of the Related Art
Silver halide photosensitive materials contain a dispersing medium mainly containing lightsensitive silver halide grains on a support. Huge researches have been made to enhance the speed of silver halide photosensitive materials. To enhance the speed of silver halide photosensitive materials, it is very important to enhance the inherent speed of silver halide grains. Various methods have been used to enhance the inherent speed of silver halide of silver halide grains. For example, performed are speed enhancement by chemical sensitizers such as sulfur, gold and the VIII group metal compound, speed enhancement by chemical sensitizers such as sulfur, gold and the VIII family metal compounds in combination with additives that promote the sensitizing effect of the sensitizers, and speed enhancement by addition of additives having a sensitizing effect with silver halide emulsion seeds. These are described in: Research Disclosure, Vol. 120, April 1974, 12008; Research Disclosure, Vol. 34, June 1975, 13452; U.S. Pat. Nos. 2,642,361, 3,297,446, 3,772,031, 3,857,711, 3,901,714, 4,266,018, and 3,904,415; and BG 1,315,755. Further, a method of reduction-sensitizing silver halide grains has been used as means for enhancing the speed. Reduction sensitization of silver halide grains are described in U.S. Pat. Nos. 2,518,698, 3,201,254, 3,411,917, 3,779,777, and 3,930,867, for example. Methods of using reducing agents are described in Jpn. Pat. Appln. KOKOKU Publication No. (hereinafter referred to as JP-B-) 57-33572 and JP-B-58-1410, and Jpn. Pat. Appn. KOKAI Publication No. (hereinafter referred to as JP-A-)57-179835, for example. Furthermore, as recently described in U.S. Pat. Nos. 5,747,235 and 5,747,236, EP's 786692A1, 893731A1, 898732A1, and WO99/05570, a sensitizing technique using an organic electron-donating compound formed of electron-donating groups and split-off groups. This method is a new sensitizing technique, and is effective for increasing speed. However, although this compound increases speed, its effect is not sufficient. Further, the compound has a defect of increasing the fog (Dmin) and deteriorates a latent-image storability, and it was strongly desired to be improved. Further, it was found that fog increases when pressure and heat are simultaneously applied to the photosensitive material in the case of using this compound.
Furthermore, recently, JP-A-2000-194085 discloses a technique of enhancing speed without deteriorating graininess, by making a silver halide photosensitive material containing at least three hetero atoms which do not react with an oxidized developing agent. However, although this method described in the publication increases the speed, this technique alone fails to produce a sufficient effect, and a further effective method for increasing speed is desired.